Effects of acidic precipitation, fertilization and liming on the ground vegetation in coniferous forests of southern Germany

Repeated vegetation surveys in non-fertilized Scots pine (Pinus sylvestris) stands with virtually constant light regimes show an increase in species number over the last 2 to 4 decades. More nitrophilic, but acid-tolerant species (e.g. Deschampsia flexuosa) have expanded mainly on loamy soils. Positive changes have also been observed with bryophytes, being indicators of better humus forms (e.g. Polytrichum attenuatum). An average decrease of cover or constancy was detected for two dwarf shrubs (Calluna vulgaris, Vaccinium vitis-idaea) and some epigeic lichens. The vegetation changes were compared with N fertilizer effects. Recovery processes after abandonment of litter removal (or grazing) and increased N-deposition are taken to be the main reasons for this change. The effects of simulated H₂SO₄ rain and liming on ground vegetation of an N-"saturated" Norway spruce (Picea abies) stand have been analyzed since the summer of 1983. The herb species Oxalis acetosella on the control plots showed very limited growth, which was removed by liming. Simulated H₂SO₄ rain (pH 2.7 to 2.8) further impaired the Ca-nutrition and growth of Oxalis and lethally damaged dominant moss species (e.g. Thuidium tamariscinum). Only a few acid-tolerant bryophytes e. g. Lophocolea heterophylla, Hypnum cupressiforme) utilized the vacated niches and increased their frequency. Liming was able to moderate or delay the acid rain effects and resulted in a slow colonization by vascular species, which are indicators of higher pH-values and increased nitrification.